Recently an automatic tag identification system such as RFID (Radio Frequency Identification) is increasingly introduced. The system comprises an information record medium of a small size referred to as “tag device”, a reading machine referred to as “reader” and a database server referred to as “backend apparatus”, and is utilized in controlling the distribution of articles. A summary of this technology will be given below.
[Processing by Tag Device]
In a basic automatic tag identification system, each tag device has a tag ID information which is inherent thereto (for example, a tag ID as prescribed by Auto-ID center of MIT comprises a manufacturer code, a goods code indicating the variety of goods and a serial number indicating the number of a particular one of goods) in storage therein. The tag device is applied to articles or the like, and the tag ID information which is inherent to each tag device is transmitted by radio communication to a reader installed in a store or the like.
[Processing by Reader]
A reader reads tag ID information from a tag device through radio communication, and sends the tag ID information to a backend apparatus to solicit an acquisition of products distribution information.
[Processing by Backend Apparatus]
A backend apparatus controls a database for ID's from each tag device and for products distribution information or the like. And the backend apparatus retrieves products distribution information or the like in the database using tag ID information transmitted from the reader as a key and transmits a result of retrieval to the reader.
[Issues in basic automatic tag identification system]
However, in the basic automatic tag identification system, anyone who is in possession of a reader can read tag ID information, and accordingly, there has been a risk that information of articles under control may leak through eavesdropped tag ID information.
As regards this, non-patent literature 2 (Stephen A. Weis, Sanjay E. Sarma, Ronald L. Rivest, Daniel W. Engels, “Security and Privacy Aspects of Low-Cost Radio Frequency Identification Systems,” First International Conference on Security in Pervasive Computing.) discloses a method in which a tag device delivers a hash value to a reader.
According to this method, the tag device initially transmits a hash value H(id |r) for a bit combination of ID information id and a random number r to the reader, which sends them to the backend apparatus. The backend apparatus forms a bit combination of the received random number r and each id′ stored in the database, and determines its hash value H(id′ |r). Then it verifies whether or not the determined hash value H(id′ |r) matches with the received hash value H(id |r), and transmits products distribution information or the like which corresponds to the matched id′ to the reader. In this manner, a leakage of the tag ID information to a third party can be prevented. It is to be noted that H(*) means a processing which applies a hash function H to *.
In a method disclosed in Japanese Patent Applications No. 2003-111342 and No. 2003-113798 which are not yet made open, a privileged ID which makes tag ID information confidential is employed to prevent a leakage of tag ID information to a third party. Specifically, in these techniques, a privileged ID is stored in a tag device, and a client apparatus which has read the privileged ID solicits a security server apparatus on a network to decrypt the privileged ID. In response to the solicitation, the security server apparatus responds with a plain text tag ID information which is a decrypted result for the privileged ID after it has confirmed that the client is a regular client apparatus. In this manner, a leakage of tag ID information to a third party can be prevented.    non-patent literature 1: EPC global, Inc., “EPC global”, [online], [retrieved Sep. 9, 2004]    non-patent literature 2: Stephen A. Weis, Sanjay E. Sarma, Ronald L. Rivest, Daniel W. Engels, Security and Privacy Aspects of Low-Cost Radio Frequency Identification Systems, First International Conference on Security in Pervasive Computing.